1. Technical Field
The present invention relates to the field of springs, and more particularly, to springs that include dual-hinges.
2. Discussion of Related Art
Physical movement is becoming recognized as an essential aid in development and maintenance of cognition:
“Cross-sectional studies have found a variety of cognitive function measures to be associated with various aspects of physical performance.”
“Cognitive Function, Gait Speed Decline, and Comorbidities: The Health, Aging and Body Composition Study”; Hal H. Atkinson, et al; The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 62:844-850 (2007) ©2007 The Gerontological Society of America 
In fact there are many who advocate that even maintaining movement in an office setting enhances performance:
“The human body is far from happy to sit still all the time! It is designed for movement” even during sitting. Using a seat that allows “hips, thighs and back [to] move . . . in the chair,” results in “fewer occupational injuries and a better work environment, fewer days off sick and greater profitability for the companies as a result.”
“The Importance of Mobility”; Lotta Jonson; Kinnarps Magazine—No. 7
The importance of movement in cognitive abilities, according to many sources, appears to be a foundation upon which a child and a young adult will be better able to receive and internalize information:
“The students' ‘workplace’ has to receive much more attention in terms of . . . ergonomic seating”, meaning seats that allow movement of hips, thighs, and back.
“What the ‘classroom of the future’ will look like”, Dr Dieter Breithecker Bundesarbeitsgemeinschaft für Haltungs—and Bewegungsförderung e. V. (Federal Working Group for Posture and Mobilization Support—Germany), 2005. (www.haltungundbewegung.de)
In addition to the above-noted advantage for adults and children to move to improve cognitive abilities, maintaining a baby in a rocking movement while in the embrace of a caregiver is known to calm the baby.
U.S. Pat. No. 5,411,315 (Greenwood) teaches a chair which moves in cyclic vertical movements while supporting an adult and infant.
A device in which the baby is placed in a bouncing chair and left alone is seen in Target.com's “Back to Nature Remote Control Bouncer” which is sold over the Internet (www.target.com).